Re: RFC: Block reservation for hugetlbfs

[David Gibson <dwg@au1.ibm.com>]

On Wed, Feb 22, 2006 at 11:38:42AM +1100, Nick Piggin wrote:
> David Gibson wrote:
> >On Tue, Feb 21, 2006 at 03:18:59PM +1100, Nick Piggin wrote:
> 
> >>This introduces
> >>tree_lock(r) -> hugetlb_lock
> >>
> >>And we already have
> >>hugetlb_lock -> lru_lock
> >>
> >>So we now have tree_lock(r) -> lru_lock, which would deadlock
> >>against lru_lock -> tree_lock(w), right?
> >>
> >>From a quick glance it looks safe, but I'd _really_ rather not
> >>introduce something like this.
> >
> >
> >Urg.. good point.  I hadn't even thought of that consequence - I was
> >more worried about whether I need i_lock or i_mutex to protect my
> >updates to i_blocks.
> >
> >Would hugetlb_lock -> tree_lock(r) be any preferable (I think that's a
> >possible alternative).
> >
> 
> Yes I think that should avoid the introduction of new lock dependency.

Err... "Yes" appears to contradict the rest of you statement, since my
suggestion would still introduce a lock dependency, just a different
one one.  It is not at all obvious to me how to avoid a lock
dependency entirely.

Also, any thoughts on whether I need i_lock or i_mutex or something
else would be handy..

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson